In radio transmission where transmitted signals from a transmitter are received at a receiver, amplitude and phase of the received signals vary over time due to Rayleigh fading involved in variations in relative positions between the transmitter and the receiver under a mobile communications environment where either or both of the transmitter and the receiver may move. In demodulation (recovering of transmitted signals) of the varying received signals in the receiver, sometimes the demodulation cannot be successfully carried out for amplitude decreasing intervals.
Among techniques for suppressing the effect of such fading variations, there is an antenna space diversity technique employing multiple antennas in a receiver, although a single antenna is commonly employed. According to the antenna space diversity technique, respective frame phases (timings) of received signals supplied from the multiple antennas are synchronized, and then the received signals are combined. By demodulating the combined received signals, the fading effect can be reduced compared to the single antenna case. In a case of two antennas, for example, if a signal received via one antenna has an insufficient level and on the other hand, a signal received via the other antenna has a sufficiently high level, level reduction can be alleviated by combining the signals received via the two antennas. Note that correlation between multiple antennas must be suppressed as much as possible for enhancing the combination effect. In addition, the combination may be carried out after weighting signals received via the respective antennas with their amplitudes. Instead of the combination of signals received via the respective antennas, a single output from an antenna having a high average level may be selected and provided.